On Sunday 09 October 2011, 15:54:14, Joachim Breitner wrote:
Hi,
Am Freitag, den 07.10.2011, 10:52 -0400 schrieb Ryan Newton:
What about just using the Data.Bits instance of Integer? Well, presently, the setBit instance for very large integers creates a whole new integer, shifts, and xors:
http://haskell.org/ghc/docs/latest/html/libraries/base/src/Data-Bits.h tml#setBit (I don't know if it's possible to do better. From quick googling GMP seems to use an array of "limbs" rather than a chunked list, so maybe there's no way to treat large Integers as a list and update only the front...)
interesting idea. Should this be considered a bug in ghc? (Not that it cannot represent the result, but that it crashes even out of ghci):
$ ghci GHCi, version 7.0.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> :m + Data.Bits Prelude Data.Bits> setBit 0 (2^63-1::Int) gmp: overflow in mpz type Abgebrochen
says info gmp: `_mp_size' and `_mp_alloc' are `int', although `mp_size_t' is usually a `long'. This is done to make the fields just 32 bits on some 64 bits systems, thereby saving a few bytes of data space but still providing plenty of range. So it seems to be GMP itself.